The present invention relates to dynamoelectric machines and methods of making the same and, more specifically to improved dc motors for commercial and industrial applications such as those utilized with golf carts, lift trucks and other industrial vehicles and methods of making such motors.
It has long been desirable to provide a direct current or universal motor having predetermined performance characteristics in a small physical size. In other words, for a motor having a specific rating, cost, and operating efficiency, it would be desirable to retain the same horsepower rating and operating efficiency while reducing the size of the various components and/or the amount of material utilized therein and thereby increase the material utilization efficiency of the motor.
Rotors formed of a stack of laminations having open slots equally spaced from one another about the periphery of each lamination for the accommodation of wire conductors are known in the prior art. However, lamination slots particularly adapted for the insertion of rectangular magnet wire heretofore have had to be sufficiently wide along the entire extent thereof (including, as is well known in the art, the slot opening or mouth) to accept the rectangular magnet wire selected for placement therein. Retaining means or wedges have usually been required to maintain the wire in position in such slots when the motor was running. It is desirable to utilize semi-closed lamination slots so that the air gap flux density will be improved as a result of smaller perturbations in the air gap flux; but the openings of semi-closed slots are typically smaller than the wire to be inserted therein, so a selected rectangular wire must either be small enough in width to pass through the slot or be inserted into the slot from the end.
Prior stator laminations and rotor laminations utilized in a specific prior art golf cart electric motor are shown in FIGS. 1-2B. The prior stator lamination 10 includes a separate yoke portion 11 and a separate pole portion 12. Each of the prior pole portions 12 comprised a plurality of stamped portions which were assembled together and then connected to the yoke 11 by various means including rivets or bolts 13. This particular stator lamination construction involved the independent manufacture of the yoke 11, the independent stamping of the pole pieces and separate manufacturing or process steps for connecting the two stator components together.
The specific geometry of the stator pole 12 restricted the flow of magnetic flux from the rotor to the stator due to the relative thin width of the stator pole tips 19. Because this restriction resulted in magnetic saturation of the lamination steel as flux flowed across the air gap from the rotor to the stator, the electrical energy required to be provided to the excitation winding around the pole had to be relatively large. The large amount of electrical energy required resulted in eight turns of rectangular copper bars (not shown) being positioned in the area between the pole tips 19 and the yoke 11.
The prior art rotor lamination 14 has sixty-three slots 15 at its periphery. In order to accept a rectangular conductor bar within the slot, the slot opening 16 had to be at least as wide as the electrical conductor but, as shown, had to be wider than the electrical conductor so that two cross-sections of the electrical conductor could fit within the slot 15 due to the decreasing width of the slot 15 from the outer periphery of the lamination toward the rotor lamination interior yoke 17. Because of the wide slot opening 16, magnetic flux transfer across the air gap into the stator poles 12 was restricted due to the smaller amount of ferromagnetic material in this prior rotor lamination tooth 18.
Because of the prior rotor lamination 14 and stator 10 geometry and their construction methods, the motor manufacturing process was expensive, and the magnetic flux transfer was inefficient.
Other arrangements are known for improving the efficiency or power output of DC and universal motors through the provision of certain slot distributions in the stator laminations, e.g., U.S. Pat. No. 3,749,956 (Reiss) issued July 31, 1973. Such stator laminations are primarily used in DC or universal motors wherein a specific relationship between the portions of the laminations is maintained in order to maintain a target efficiency. Specifically, U.S. Pat. No. 3,749,956 teaches that each lamination slot should have a depth dimension which is at least approximately three times the maximum width dimension of the slot; that each portion of the yoke should have a width adjacent each slot which is equal to at least 1.1 times the width of the adjacent portion of the slot; that the depth of each slot should be at least 1.25 times the width of the root portion of the poles; and that the distance from the center of the yoke to the deepest part of each slot should be a maximum of 1.3 times the depth of each slot. The '956 patent alleges that the physical dimensions of a stator constructed according to the teachings of the patent can be less than the physical dimensions of a conventional stator having the same efficiency and output characteristics.
Other patents which disclose various armatures and stator designs include U.S. Pat. No. 3,643,118 (Ichiki et. al.) issued Feb. 15, 1972; U.S. Pat. No. 2,715,690 (Neuenschwander) issued Aug. 16, 1955; and U.S. Pat. No. 2,298,388 (Knobel) issued Oct. 13, 1942.
Notwithstanding the presentations of the art discussed above, there continues to be a need for improved motors and methods of making motors and their various components. Such motors desirably would provide the same and/or greater horsepower rating and operating efficiency while reducing both the size and weight of the motor; would have a rotor lamination having semi-closed slots with relatively narrow slot openings for receiving rectangular conductor members having relatively large widths therein; would have a one piece stator lamination; would have a stator lamination which provides an optimized path for magnetic flux therethrough; would have a reduced outer diameter without significant length increase; and would have increased horsepower and efficiency per unit weight and per unit volume.